A series of in vivo and in vitro experiments are to be conducted to test the hypotheses that prostacyclin (PGI2) plays a luteotropic role in the control of corpus luteum function and that thromboxane (TXA2) plays a luteolytic role. The possible existence of a neurohumoral control mechanism, involving gonadotropin releasing hormone (GnRH) of extra-hypothalamic origin, will also be studied. In vivo experiments to test the roles of PGI2 and TXA2 in bovine corpus luteum function include measurements of the stable metabolites of these compounds (6-keto-PGF1 alpha and TXB2) in ovarian arterial, uterine venous, ovarian venous and jugular blood during the estrous cycle and after administration of hormones known to cause luteal regression (oxytocin, estradiol, PGF2 alpha) and administration of specific inhibitors of PGI2 and TXA2 synthesis. In vitro experiments include studies of the control of myometrial, endometrial and ovarian production of PGI2 and TXA2. Recently developed techniques for dispersing and separating luteal cells into distinct sub-populations will be used in the in vitro studies of PGI2 and TXA2 production by the corpus luteum. In vivo experiments to study the role of GnRH in corpus luteum function include assessment of luteal function after infusions of GnRH directly into a branch of the ovarian artery, into the uterus or into the jugular vein; GnRH antiserum will also be infused into the ovarian artery, and a potent GnRH analog will be given over an extended period of time. Measurements of GnRH will be made in concurrently collected uterine venous, ovarian arterial and jugular samples. In vitro studies include experiments on the effects of GnRH on basal and LH-stimulated progesterone production by dispersed luteal cells and immunocytological studies to indicate the sites of production of GnRH.